432 
K AM AK ICH l KLSHINOUYE : 
Key to the families of the order Plecostei. 
Body wholly covered with scales, second dorsal and anal high, vertebrae 18 f 21, 
transverse process present, 1st vertebra short, ancliylosed to the skull, alis- 
phenoids meet at the ventral median line, air-bladder generally present. Thunnidae. 
Body naked outside of the corselet, second dorsal lower than the first, 
vertebrae generally 20 + 19, some intermuscular bones are divided into two, 
distal and proximal, epihaemal spine developed between the centrum and 
the haemal arch in most vertebrae, network of l.aemal processes well 
developed, air-bladder wanting.. . . Katsuwonidsie- 
Family THUNNIDAE Kisliinouye. 
Thunnidae, Kishinouye, 1918. 
Body plum]), wholly covered with scales, which differ in size and form in 
different parts of the body. Corselet well developed, but its boundaiy is not 
distinct. The lateral line has a peculiar curve above the pectorals. Teeth 
rather feeble. Single series of small conical teeth in both jaws. They are sharp 
and'curve inward. A filiform teeth on the vomer, palatines, and pterygoids. Many 
dentigerous calcareous plates are found on the palate. The denticles on these plates 
are quite similar to those found on the vomer, palatines and pterygoids. Thus 
the roof of the moutli-cavity is quite rough, contrary to the nearly smooth roof in 
the Katsuwonidae. Three lobes of the liver subequal. Intestine rather long, with 
three folds. Pyloric tubes developed only on the posterior convex side of the 
duodenum. Pyloric coeca heteroclitic, irregular in size. Those found at the 
distal end being longer and thicker than those at the proximal part. This 
heterochrony is more marked in primitive forms. Rectum short, it has nearly 
the same diameter as the preceding pari of the intestine. Air-bladder present, 
except in Neothunnus rams. 
Cutaneous blood-vessels above and below the lateral median hue are imited 
both at the anterior and posterior ends, and are connected by short horizontal 
vessels with the chief blood-vessels in the liaemal canal at the caudal peduncle. 
Hie cutaneous veins are large and unite with the Cuvierian ducts directly or with 
the cardinal vein. Each of the paired cutaneous arteries arises just beliind the 
pharyngeal muscles or somewhat beliind it, runs backwards and downwards 
beliind the root of either the third or fifth rib, and is divided into two nearly 
parallel branches, a little before it comes to the surface of the muscle, between 
two consecutive intermuscular bones. The dark red portion of the lateral 
